The rotameter is one of the better known flowmeters belonging to the family of so called "variable area" flowmeters and has wide application in measuring flows in various industries and scientific laboratories. In today's automated industrial and scientific operations extensively using computerized processes and controls, a flowmeter must have a readout device that provides the information on the measured values of flow rate in the form of an electrical signal, whereby the information on the flow rates can be fed into a data processing computer or other process controlling device as an input. While the rotameter of the present day technology provides a reliable and accurate means for measuring the flow rates of fluid media in an economic manner, most of the rotameters available at the present time are designed for visual readout only and do not have a readout device providing the measured values of flow rates in the form of an electrical signal and consequently, they are not suitable for taking data which can be directly fed into a computer or other process controlling device. A few versions of the present day rotameter with readout devices providing the measured flow rates in the form of an electrical signal usually lack accuracy as well as reliability. The present day rotameter measures the dynamic pressure of the fluid flow, that is equal to one half of the fluid density times the square of the fluid velocity. In order to determine the mass or volume flow rate of the fluid from the dynamic pressure measured by a rotameter, the fluid must have a density of known value or an apparatus measuring the fluid density must be installed in conjunction with the rotameter.